JPH09262500A - Electrical precipitator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent dust particles from rescattering from a dust collecting electrode in an electrical precipitator for air cleaning. SOLUTION: DC high voltage V is applied between a dust collecting electrode 41 and a counter electrode 45 to collect charged dust particles on the dust collecting electrode 41. In the whole area of the surface of the dust collecting electrode 41, a lot of minute projecting parts 43 are provided at minute intervals to form an unequal electric field near the surface of the dust collecting electrode. The smaller the radius of curvature R of the projecting part, the better. It is desirable that the distance L between the adjoining projecting parts is sufficiently narrow so that there may exist no clearance in which the unequal electric field is not formed. Practically, it is preferable that R<=0.1mm and L/R=2∼4. As the dust collecting electrode, a flat metal plate in which a part thereof the cut and raised or that in which slits are arranged, or an insulating board on which lattice-shaped print wiring is formed, or a metal net, or a dielectric arranged between two counter electrodes forming a strong electric field in a float state, or a metal fiber net may be used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrostatic precipitator for air cleaning.

[0002]

2. Description of the Related Art An electrostatic precipitator is widely known in which ionic wind is generated by corona discharge and floating particles are charged and separated and removed by electrostatic force.

For example, Japanese Examined Patent Publication No. 6-36875 discloses air using an electrostatic precipitator in which an ionizing wire (discharge electrode), a dust collecting electrode and a counter electrode are arranged at predetermined positions so as to achieve the above-mentioned operation. A purifier is disclosed. This technology is
A DC high voltage is applied between the discharge electrode and the counter electrode and the dust collecting electrode to generate a corona discharge, which ionizes and charges the molecules and suspended particles in the air passing therethrough, and the collision energy of the ions to the molecules. Generate an ion wind to guide the charged particles into the space between the counter electrode and the dust collecting electrode, and apply a high voltage between the counter electrode and the dust collecting electrode to form a strong electric field. The charged particles are collected by the dust collecting electrode by the Coulomb force by the.

[0004]

The electrostatic precipitator having such a structure is widely used as an ion type air cleaner without a fan because air flows by the ionic wind.

However, particles of 0.1 to several microns such as air dust and cigarette smoke, which are most abundant in the living space, lose their electric charge when they are collected by the dust collecting electrode, so that the cloning force does not work and the dust collecting electrode There is a case that it is separated from and re-scatters in the air.

An object of the present invention is to provide an electrostatic precipitator capable of preventing re-scattering of particles collected by a dust collecting electrode.

[0007]

The present invention is characterized in that the dust collecting electrode is constructed so that an unequal electric field is formed in the vicinity of its surface.

As a result, not only the Coulomb force with respect to the charged particles but also the gradient force due to the electric field gradient (electric field gradient) in the non-uniform electric field acts near the surface of the dust collecting electrode. The gradient force is a force that causes unbalanced polarization of particles due to an electric field gradient in an unequal electric field and attracts the particles in a strong electric field direction, and works even if the particles are not charged. Therefore, even if the particles collected by the dust collecting electrode lose the charge, they remain attracted to the dust collecting electrode by the gradient force.

One example of the structure of the dust collecting electrode for forming the non-uniform electric field is to provide a plurality of convex portions on the surface. The lines of electric force directed from the counter electrode to the dust collecting electrode are focused on the convex portion, so that the lines of electric force can be coarse and dense in the vicinity of the convex portion. Therefore, a gradient of the electric field strength is generated in the vicinity of the convex portion of the dust collecting electrode, and the gradient force is further applied to the charged particles attracted by the Coulomb force to the vicinity of the convex portion.

The smaller the radius of curvature R of the convex portion, the better,
Further, it is desirable that the distance L between the adjacent protrusions is sufficiently narrow so that there is no gap between the protrusions where an uneven electric field is not formed. As a condition that satisfies this, L / R
= 2-4 is preferable.

Another example of the structure of the dust collecting electrode is a mesh of conductors, for example, a metal mesh. In this case, the line radius of the net should be as thin as possible, for example 0.1 mm or less. Since the lines of electric force are focused on each grid line of the net, an unequal electric field is formed near the net, and a gradient force is generated there.

As still another example, the dust collecting electrode may be provided with a plurality of cut and raised portions or a plurality of slits. The lines of electric force are focused on the cut-and-raised part or the edge part of the slit to form an unequal electric field.

Alternatively, the printed wiring of the conductor may be formed in a grid pattern on the insulating substrate and used as a dust collecting electrode.
The lines of electric force are focused on the edges of the printed wiring and form an unequal electric field.

In still another configuration example, a fiber assembly or net of a dielectric material or a conductor material is arranged in an electrically floating state as a dust collecting electrode between at least two counter electrodes to which a voltage is applied. . In this case, due to the polarization effect of the dielectric or conductor, the lines of electric force are focused on each lattice line of each fiber or net, and an unequal electric field is generated in the vicinity thereof.

It is desirable that the above-mentioned cut-and-raised portions, slits, grid lines of printed wiring, grid lines of meshes or fibers are also sufficiently narrow so that there are no gaps in which an unequal electric field is not formed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the electrostatic precipitator of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the principle of the dust collecting electrode of the present invention.
A convex portion 3 is provided on the surface of the flat plate type dust collecting electrode 1 as a whole, and a direct current is provided between the dust collecting electrode 1 and a flat plate type counter electrode 5 which is arranged in parallel to face the dust collecting electrode 1. High voltage V
Is applied, an electric field E is generated by the line of electric force as shown by the arrow in the figure.
Occurs.

Except in the vicinity of the convex portion 3, the lines of electric force flow in parallel with equal density and form a uniform electric field. The charged particles having the electric charge Q that have entered the uniform electric field receive the Coulomb force (= EQ) in the direction of the electric force line and move toward the dust collecting electrode 1.

In the vicinity of the convex portion 3, the lines of electric force are focused toward the convex portion 3 as shown by the arrow in the figure.
The electric field gradient (gradient,
An unequal electric field having a strength difference). The charged particles 7 that have reached the unequal electric field due to the action of the Coulomb force are subjected to the strong Coulomb force, that is, the gradient force toward the direction of the convex portion 3.

This gradient force F (vector) is
It is generally known that it can be expressed by the following equation due to the gradient of the electric field E (vector).

[0021]

[Equation 1]

[Equation 2] Here, a is a particle diameter, εr is a relative permittivity of particles, and εm is a relative permittivity of air (medium).

The gradient force F in the vicinity of the convex portion 3 shown in FIG. 1 is calculated by the following equation.

[0023]

(Equation 3) Here, R is the radius of curvature of the convex portion, and d is the distance of the charged particles from the flat plate surface.

As can be seen from this equation, the gradient force F increases as the particle diameter a and the relative permittivity εr of the particles increase.

According to the calculation, when the particle diameter a becomes larger than about 0.2 μm, the gradient force suddenly becomes large. Therefore, particles such as air dust, cigarette smoke, etc., which have a lot of living space, having a particle diameter of 0.1 to several microns It can be expected that the gradient force will work effectively.

Further, the gradient force F increases as the radius of curvature R of the convex portion decreases, and the gradient force F decreases rapidly as the distance d from the center of the convex portion increases.

FIG. 2 is a relational curve between the distance d from the convex portion and the gradient force F with the radius of curvature R of the convex portion as a parameter, which is obtained from the equation (3). As environmental conditions, an electric field E = 1.0 MV / m, a particle diameter a = 1.0 μm, and a relative dielectric constant εr = 4 of the particles are selected.

From this graph, it can be seen that a large gradient force F acts within the range where the distance from the surface of the convex portion of the particle corresponds to the radius of curvature R, but if the distance is farther than this, the gradient force F rapidly attenuates.

Further, even if the particles collected on the surface of the convex portion lose the charge and become 0e, for example, when the radius of curvature R is 0.1 mm, the gradient force F on the surface of the convex portion is 1.5 ×
It is 10 ^-13 N. This is the same electric field strength E = 1.0 MV /
It is almost the same value as the Coulomb force of 1.6 × 10 ^-13 N acting on a charged particle having a charge of 1e (= 1.6 × 10 ^-19 Coulomb) in m. Experimentally, it has been found that particles having a charge of 1e are adsorbed and held by the dust collecting electrode.

Therefore, it can be seen that even if the particles trapped in the convex portion having the radius of curvature R of 0.1 mm or less lose the electric charge, a gradient force sufficient to attract and hold the dust collecting electrode is exerted. From this, if a convex part with a radius of curvature of 0.1 mm or less is provided,
It can be seen that the gradient force can be effectively used.

Further, the re-scattering phenomenon tends to occur as the particle diameter becomes larger, but as can be seen from the equation (3), the gradient force F becomes larger as the particle diameter a becomes larger, so that it acts more effectively on large particles. To do.

Next, an experiment was conducted to find out on which surface of the convex portion the gradient force works most strongly. FIG. 3 is a diagram showing the gradient force measurement position of the convex portion, and the gradient force in three directions, that is, the direction perpendicular to the electrode surface (a), the direction 45 degrees from the electrode surface (b) and the direction parallel to the electrode surface (c). F was measured. The lines of electric force are assumed to flow as shown by the arrows in the figure.

4 (a), (b) and (c) are characteristic curves of the gradient force F measured in the directions of (a), (b) and (c) of FIG. Show as.

From this figure, the gradient force F is smallest on the convex surface in the direction (a) perpendicular to the electrode surface (see FIG. 4).
(A)), it can be seen that the gradient force F in the direction (c) parallel to the electrode surface is the largest (FIG. 4 (c)). Therefore,
When a large number of convex portions are arranged on the electrode surface, it is important to arrange the convex portions at appropriate intervals so that the gradient force F in the parallel direction of each convex portion can be effectively utilized. That is, if the spacing between the convex portions is too wide, an unequal electric field is not formed between the convex portions, and there is a gap in which no gradient force is generated,
The spacing should not be too wide.

According to the experimental result shown in FIG. 4 (c), it is observed that the gradient force is rapidly attenuated when the distance from the surface of the convex portion exceeds the radius of curvature R. From this, it can be said that the range where the gradient force of each convex portion effectively works is within a distance corresponding to the radius of curvature R from the surface of the convex portion. Therefore, the distance between the centers of the protrusions is L
Then, it is desirable to select the interval of the convex portions within the range of L / R ≦ 4. On the other hand, it is necessary that L / R> 2 so that the convex parts do not mechanically overlap each other. From the above, the relationship between the radius of curvature R of the convex portion and the convex portion center interval L is L / R
= 2-4 is desirable.

It should be noted that the intervals between the convex portions are not necessarily all constant, and the intervals between the convex portions may vary within the range of the above conditions.

If a large number of convex portions are formed on the surface of the dust collecting electrode so as to satisfy such conditions, an uneven electric field is evenly formed on the entire surface of the dust collecting electrode, and a gradient force is generated on almost the entire surface of the dust collecting electrode. The particles collected by the dust collecting electrode can be adsorbed and held on the dust collecting electrode.

Further, not only re-scattering occurs when charged particles are collected by the dust collecting electrode and loses electric charge, but also high resistance particles (10 ⁸ Ωm or more) such as cigarette smoke are reverse corona between the dust collecting electrode and the dust collecting electrode. Reverse ionization and re-dispersion caused by the occurrence of discharge and recharging of the particles to the anti-power generation level, and low resistance particles such as metal powder (100Ω
(m or less) is charged to the same potential as the dust collecting electrode, and the phenomenon of induced re-scattering caused by repulsive force can also be reduced by the above-mentioned gradient force.

Further, the speed w at which the charged particles move to the electrode surface.
Is represented by the following equation.

W = F / 6πaμ (4) where F is the sum of the gradient force and the Coulomb force,
a is the particle diameter, and μ is the viscosity of air.

From the equation (4), it is predicted that the moving speed w of the particles to the dust collecting electrode, that is, the dust collecting speed is increased by the large gradient force F in the vicinity of the dust collecting electrode, and the re-scattering from the electrode is prevented. Together with this, improvement of dust collection efficiency can be expected.

Next, specific embodiments of the present invention will be described.

FIG. 5 shows the first embodiment, in which a net of conductors such as a metal net is used as the dust collecting electrode. A high DC voltage V is applied between the metal net 11 which is a dust collecting electrode and the counter flat plate electrode 13. Due to the action of ion wind or the like due to corona discharge at a fan (not shown) or a discharge electrode (not shown), air containing dust is generated between the electrodes 11 and 13 as indicated by arrows in the figure.
Is almost parallel to.

It is desirable that the grid of the metallic net 11, that is, the net wire is as thin as possible, for example, 0.1 mm or less, and the pitch of the net wire is as narrow as possible, for example, 0.2 mm or less. With such a configuration, a uniform electric field is formed between the metallic net 11 and the opposing flat plate electrode 13, but in the vicinity of the metallic net 11, the lines of electric force are focused on each net wire and the electric field lines are not formed. Since a uniform electric field is formed, the dust particles are adsorbed and held by the metal net 11 by the action of preventing re-scattering due to the gradient force in the non-uniform electric field.

FIG. 6A shows the second embodiment, in which a high DC voltage V is applied between the two opposed plate electrodes 21 and 23. The dust collecting electrode 25 is arranged between the two electrodes 21 and 23 in parallel to them without applying a voltage, that is, in an electrically floating state. The air flow direction is substantially parallel to the electrodes as in the first embodiment. Here, the dust collecting electrode 25 is a net woven with a dielectric (eg, glass fiber, resin fiber, etc.),
It is a fiber aggregate, paper or cloth.

Each fiber or mesh wire of the dust collecting electrode 25 is polarized by the electric field between the counter electrodes 21 and 22, and
As shown in (b), the lines of electric force are focused on each fiber or each mesh wire. As a result, an unequal electric field is generated in the vicinity of the dust collecting electrode 25, and a gradient force is generated in this part. Therefore, the particles collected by the dust collecting electrode 25 are prevented from re-scattering. Further, the use of such a net-like or fiber-aggregate dust collecting electrode 25 also has an effect as a mechanical filter for mechanically collecting dust particles.

Even if a metal net or a fiber aggregate is used for the dust collecting electrode 25, the metal has a dielectric constant which is regarded as infinite, so that a remarkable polarization occurs. Therefore, the same effect as described above can be obtained. However, it is desirable to use an insulation-coated metal mesh because metals carry the risk of discharge when placed in a strong electric field.

Therefore, the net-like dust collecting electrode 25 of the second embodiment is made of a material having a high dielectric constant and a high surface resistance or insulation resistance, and the pitch of the net wires or fibers is the same as that of the first embodiment. It is desirable to use the same conditions.

FIG. 7 shows a third embodiment, in which the dust collecting electrode 3
In No. 1, the surface of a metal flat plate is roughened by sandblasting, chemical etching, plasma etching or the like, and a large number of uneven portions 33 are provided on the entire surface of the electrode. It is desirable that the size and interval of the convex portions be within the above range.

If a high DC voltage V is applied between the dust collecting electrode 31 having an uneven surface and the counter flat plate electrode 35, the dust collecting electrode 3
An unequal electric field is formed in the vicinity of the uneven portion 33 of No. 1 and a gradient force is generated, and particles in the vicinity are adsorbed and held by the dust collecting electrode.

FIG. 8A shows a fourth embodiment, in which the dust collecting electrode 41 is obtained by press working from the back surface of a metal flat plate, and a large number of convex portions 43 are provided on the front surface at minute intervals. When a DC high voltage V is applied between the dust collecting electrode 41 and the counter plate electrode 45, the lines of electric force are focused on the convex portion as shown in FIG. 8B, and a gradient force is generated at this portion.

FIG. 9A shows a fifth embodiment, in which the dust collecting electrode 51 is obtained by cutting and raising a large number of finely spaced portions of a metal plate toward the counter electrode 53 side.
When a high DC voltage V is applied between the two, the lines of electric force are focused on the cut-and-raised portion 53 to generate a gradient force, as shown in FIG. 9B.

FIG. 10A shows a sixth embodiment, and the dust collecting electrode 61 is as shown in the detailed detailed view of FIG. 10B.
A grid-shaped printed wiring 67 is formed on the insulating substrate 65. When a high DC voltage V is applied between the dust collecting electrode 61 and the counter plate electrode 63 formed in this way, the lines of electric force are focused on the edge portion of the printed wiring 7, as shown in FIG. A gradient force is generated on the surface of the electrode 61.

FIG. 11A shows a seventh embodiment, in which the dust collecting electrode 71 is obtained by punching a metal flat plate and providing slits 73 at minute intervals.
When a high DC voltage V is applied between the two, the lines of electric force are focused on the edge portion of the slit 73 and a gradient force is generated on the surface of the electrode 71, as shown in FIG.

Although some embodiments have been described above, the present invention is not limited as long as the dust collecting electrode is constructed so that an unequal electric field is formed over at least a part of the surface of the dust collecting electrode. However, the present invention is not limited to the contents of the above-described embodiment, and can be carried out in various modified, improved, and modified modes.

In the embodiment described above, since the dust collecting electrode is set to a positive potential, when a corona discharge is generated by a discharge electrode (not shown) to charge the dust particles, a negative corona that charges the particles to a negative potential is used. Will cause a discharge,
In order to suppress the generation of ozone, a positive corona discharge may be used to bias the dust collecting electrode to a negative potential.

[0057]

As described above, according to the present invention,
It is possible to prevent the particles collected on the dust collecting electrode from re-scattering.

[Brief description of drawings]

FIG. 1 is a principle diagram of a dust collecting electrode of the present invention.

FIG. 2 is a characteristic curve of gradient force obtained by theoretical calculation.

FIG. 3 is a diagram showing a measurement position of a gradient force of a convex portion.

4 is a characteristic curve of gradient force at each measurement position in FIG. 3, where (a) is a direction perpendicular to the electrode surface, (b) is a direction at 45 degrees with the electrode surface, and (c) is parallel to the electrode surface. Shows the gradient force in the direction.

FIG. 5 is a configuration diagram of the first embodiment using a metal net dust collecting electrode.

FIG. 6A is a configuration diagram of a second embodiment using mesh-shaped dust collecting electrodes arranged in parallel between opposed electrodes, and FIG. 6B is a diagram showing focusing of lines of electric force.

FIG. 7 is a configuration diagram of a third embodiment in which a metal flat plate is blasted to use a dust collecting electrode having an uneven portion.

FIG. 8A is a configuration diagram of a fourth embodiment using a dust collecting electrode having a convex portion formed by pressing a metal flat plate, and FIG. 8B is a diagram showing focusing of electric force lines.

9A is an electrode configuration diagram of a fifth embodiment using a dust collecting electrode obtained by cutting and raising a part of a metal flat plate, and FIG. 9B is a diagram showing focusing of electric force lines.

FIG. 10A is a configuration diagram of a sixth embodiment using a dust collecting electrode in which a grid-like printed wiring is provided on an insulating substrate,
(B) is a detailed view of a printed wiring part, and (c) is a view showing focusing of lines of electric force.

11A is a configuration diagram of a seventh embodiment using a dust collecting electrode in which a metal flat plate is punched and slits are provided at minute intervals, and FIG. 11B is a diagram showing focusing of lines of electric force.

[Explanation of symbols]

1 Dust collecting electrode 3 Convex part 5, 13, 23, 35, 45, 55, 63, 75 Opposed plate electrode 7 Charged particle V DC high voltage 11, 21, 25, 31, 41, 51, 61, 71 Dust collecting electrode 33 Concavo-convex part 43 Convex part 53 Cut and raised part 65 Insulating substrate 67 Printed wiring 73 Slit

Front page continuation (72) Inventor Yasuo Hamada 2-1-1 Nakajima, Kokurakita-ku, Kitakyushu, Fukuoka Prefecture Totoki Equipment Co., Ltd. (72) Kiyoshi Fujino 2-1-1, Nakajima, Kitakyushu, Kitakyushu, Fukuoka No. 1 Totoki Equipment Co., Ltd.

Claims (11)

[Claims] 1. An electrostatic precipitator that collects dust on a surface of the dust collecting electrode by forming an electric field between the dust collecting electrode and a counter electrode arranged to face the dust collecting electrode. An electrostatic precipitator having a structure in which an unequal electric field is formed near the surface. 2. The electrostatic precipitator according to claim 1, wherein the dust collecting electrode has a plurality of convex portions on the surface. 3. The electrostatic precipitator according to claim 1, wherein the dust collecting electrode has a mesh conductor. 4. The electrostatic precipitator according to claim 1, wherein the dust collecting electrode has a plurality of cut and raised portions. 5. The electrostatic precipitator according to claim 1, wherein the dust collecting electrode has a plurality of slits. 6. The electrostatic precipitator according to claim 1, wherein the dust collecting electrode has an insulating substrate and a grid-shaped printed wiring formed on the surface of the insulating substrate. 7. The electrostatic precipitator according to claim 1, comprising at least two counter electrodes to which a voltage is applied, wherein the dust collecting electrode is a fiber assembly or a mesh of a dielectric or a conductor. And an electrically precipitator which is disposed in an electrically floating state between the at least two opposed electrodes. 8. The electrostatic precipitator according to any one of claims 2 to 7, wherein any of the convex portion, the cut and raised portion, the slit, the grid of the printed wiring, the grid of the mesh and the fiber of the fiber assembly. The electrostatic precipitator is characterized in that the intervals are such that there is no gap where there is no unequal electric field. 9. The electrostatic precipitator according to claim 2, wherein the radius of curvature R of the convex portion and the interval L between the adjacent convex portions.
An electrostatic precipitator characterized by having a ratio of approximately L / R = 2-4. 10. The electrostatic precipitator according to claim 2, wherein the convex portion has a radius of curvature of 0.1 mm or less. 11. The electrostatic precipitator according to claim 3, 7, or 8, wherein the wire radius of the mesh of the mesh or the fibers of the fiber assembly is 0.1 m.
An electrostatic precipitator characterized by being less than m.